If the concrete surface is scratched or varnished, you should re-stain it. So, how to do it?
You can restain concrete if the surface isn’t defective or filthy. However, if the old finish is filthy or damaged by moisture, you must remove it before re-applying a new one.
To restain the concrete, sand the surface with fine-grit concrete sandpaper. Sanding will remove imperfections and bumps from the surface, increasing the bonding between concrete and stain.
Also, if the concrete stain is sealed, you must remove the sealer first. That’s because the sealer will prevent the new coating from sticking.
You can restain colored concrete, but you must use acid stain to get the best results. If you use regular stain, the stain won’t penetrate the old finish. That’s because of the hard nature (texture) of the concrete.
Also, you must use the same (or similar) color because new coating won’t penetrate the old coating, so the colors will mix. As a result, the finish will appear lighter than it is. The finish will look unprofessional and unfinished if you use a dark-colored over a light-colored stain.
To cover the old color shade, you must apply 3-4 coats of stain, but applying that many coats isn’t recommended as the finish becomes too thick. So, you must apply a stain-blocking primer between both finishes (old and new) to prevent bleed-through.
How To Restain Concrete?
Here are a few things you need to know:
- If the existing finish is sealed, you must remove the sealer first.
- Acid-stains work best on concrete.
- Sand the existing finish to allow the new stain to stick better.
- It’s better to remove damaged finishes than staining over them.
- It’s better to use the same color.
Here are the tools you need:
- Concrete sandpaper
- A gallon of acid stain for concrete
- Paint thinner
- A degreaser or concrete cleaner
- A pair of gloves
- A paintbrush or spray gun
- An acrylic-based sealant
1. Clean and Degrease The Concrete
First, clean and remove grease, oils, and dirt from the existing concrete stain.
To clean it:
- Use rubbing alcohol, TSD, white spirits, or concrete clear.
- Apply the solvent over the concrete.
- Use a soft brush to scrub (remove) the dirt.
- Remove the solvent residue with warm water.
- Don’t use too much water because concrete will take longer to dry.
2. Sand The Finish
Once the concrete is dry, sand it. Sanding will remove bumps and imperfections and allow the new coat to stick better. To sand concrete, use fine-grit concrete sandpaper.
If the finish is sealed (has a topcoat), you must remove it first because it will prevent the new coating from penetrating the surface and sticking. This leads toa sticky finish.
To remove the sealant, use a paint-removing compound.
3. Apply Acid Stain
Once the concrete is sanded and has no sealer, you can apply a primer (or concrete paste). The primer will prevent bleed-through and help the new coating from sticking better.
If you are changing the color of the finish, applying primer is necessary. However, if you are using the same color shade as the existing finish, priming is optional.
Once the surface is cleaned, sanded, has no sealer, and is primed (optional), apply 3 coats of the acid stain. Wait until one coat dries before applying the new one It takes acid stain 5-24 hours to fully dry.
4. Seal The Stain (Optional)
To increase the durability of the finish, seal it with a top coat. When dry, a sealer will produce a glossy moisture-resistant layer that protects the finish from water, moisture, scratches, and damage.
However, a sealer can change the color shade of finish. For example, if you use polyurethane, the stained concrete will appear lighter. But, if you use wax, it will appear darker.
Staining Over Acid-Stained Concrete
You can’t stain over acid-stained concrete because the acid stain will prevent a new coating from sticking. Acid stains set (penetrate) into the concrete surface pores. So, when you apply it, the coating will etch and “eat” into the concrete material, and then the color will set inside the surface.
So, if you apply a regular stain over it, its coating won’t stick because it can’t penetrate the surface, Since it can’t penetrate a surface, the coating (and finish) will turn sticky.
To stain over acid-stained concrete, you must apply a primer or paste, or remove the finish first. The primer or paste will act as a smooth undercoat for the new coating to stick to.
You can also apply an acid stain with the same color shade. The new finish will look better and will stick. However, you should avoid using oil-based stain over an acid stain finish as they aren’t compatible.
How Long Does it Last?
Stains last between 18 months and 4 years on concrete. The finish doesn’t last long because stains (by design) aren’t durable and are designed to enhance the surface’s color and not protect it.
So, stain makes a surface look better, but it won’t protect it. If the surface is exposed to heavy usage, foot traffic, or water, the finish will start to wash off.
However, you can increase its durability by sealing it. When you seal it, the sealant will dry to form a hard moisture-resistant film that protects the finish from water, moisture, and scratches. On average, a sealed stain finish lasts up to 6 years on a concrete surface. Stains sealed with 2-part epoxy can last over 8 years.
You can restain concrete, but you must use the same type of concrete stain (and color) or use a primer between two coats. Also, if the finish is sealed, you must remove the sealer.
Tony is a professional painter and an author of DIY Geeks. Tony has completed over 1,000 painting projects for his clients. It's safe to say he knows what he Is talking about,